MONTPELIER — The amount of power that utilities could buy from customers with solar or other renewable energy systems would nearly quadruple under a measure given preliminary approval by the Vermont Senate.

Vermont caps the amount of power utilities can take through what’s called net metering, when the owners of rooftop solar installations or similar projects put excess power onto the grid.

The current cap says each utility can take up to 4 percent of the peak load on its system from net-metering projects. The bill increases that to 15 percent.

“Net metering projects are very popular in the state, and they’re popular because of the programs we have to encourage this kind of development,” Sen. Virginia Lyons, D-Chittenden, said in explaining the proposed expansion to her colleagues Thursday.

Utility customers who participate in net-metering get paid at above retail rates for the power. While typical retail rates among Vermont utilities run less than 15 cents per kilowatt hour, net-metered customers are paid 20 cents per kwh for their power.

The bill would change that to 19 cents for projects with a capacity more than 15 kilowatts. After 10 years, participants in the program would be paid the retail rate for their power.

Critics have complained that net metering is too expensive and drives up electric rates; its defenders say renewable energy development is important to the battle against climate change and needs to be encouraged. They also argue that net metering actually lowers costs in many instances because it enables utilities to avoid building capacity for larger peak loads.

The Senate rejected an amendment offered by Sen. Kevin Mullin, R-Rutland, to have net metering participants paid the same rate that utilities pay to other sources at wholesale, prices that usually average well below 10 cents per kwh.

A kilowatt is a volume of power delivered at an instant; a kilowatt-hour is that volume of power delivered continuously during the course of an hour.

An amendment added by the Senate after the House passed the bill earlier this year is designed to encourage municipalities to build solar-power projects on former landfills.